US2778506A - Hoist mechanisms - Google Patents

Description

Jan. 22, 1957 R. J. HARRY 2,778,506

HOIST MECHANISMS Filed June 29, 1953 INVENTOR.

Robert J. Hurry BY M '7 HOIST MECHANISMS Robert J. Harry, Alliance, Ohio, assignor to The Alliance Machine Co., Alliance, Ohio, a corporation of Ohio Application June 29, 1953, Serial No. 364,635

4 Claims. (Cl. 212-21) This invention relates to hoist mechanisms and particularly to a crane hoist. Crane hoists, and particularly electric overhead traveling cranes, are used in many industries both within and outside of buildings for picking up and transporting heavy loads from one part of a plant to another. Generally such hoists are provided with a framework carrying a hoisting drum driven by a motor. The hoisting drum is, in turn, provided with hoisting ropes depending therefrom and carrying a lifting block, usually provided with a book. The motor is usually electrically operated and provided with a limit switch actuated by the lifting block as it approaches the hoisting drum to disconnect the motor and prevent overtravel of the block.

The motors customarily used on hoisting cranes, particularly those used in the steel mills of this country, are series wound and the speed varies inversely as the load. Under light load or no-load conditions, the armature frequently attains a speed of 2 /2 times the half-hour rating of the motor. Since the energy in the revolving parts varies as to the square of the speed, the kinetic energy stored up in the revolving parts would be the square of 2 /2 or 6 /2 times the half-hour rating of the motor. In a typical example a motor having a speed of 400 R. P. M., based on the half-hour rating, would have 10,505 ft. lbs. of kinetic energy stored in the revolving parts of the hoist. The kinetic energy built up in the revolving parts of such a crane will, if the motor is not stopped prior to the time the lifting block reaches the top of its travel, bring the lifting block against the lifting beam of the crane with such force that the hoisting ropes will break, dropping the lifting block to the floor, often with fatal results.

The most common cause of rope breakage is the acci dental failure of the hoist limit switch when raising the empty lifting block at full speed. When the limit switch fails under such conditions the hoist motor is revolving at two to three times normal speed and possesses tremendou inertia as pointed out above. It is therefore obvious that when the hook block engages the upper sheave beam of the frame, rope breaking forces are applied before the circuit breaker is kicked out and the motor brought to rest. It is impossible to drain off the inertia of the motor in zero or near zero time without rope-breaking stresses.

I provide a crane hoist mechanism which absorb this storedfup kinetic energy and successfully avoids the difiiculties mentioned above characteristic of hoist mechanisms heretofore used. In a preferred embodiment I provide a crane mechanism comprising a frame, a lifting block depending from said frame, means on the frame raising and lowering said lifting block relative to said frame and resilient means between the frame and the lifting block absorbing the kinetic energy of the raising and lowering means and the moving lifting block when the block is brought against the frame by the raising and lowering means. ireferably the resilient means are a series of springs mounted on the lifting block and supporting a striking plate which engages the frame to transmit the energy of the moving parts to the springs at whatever angle the lifting block approaches the frame. Since the I trically-operated crane.

lifting block may approach the frame while swinging as a pendulum therebelow this feature of the present invention is important and unique. The resilient means may, however, be mounted on the frame and depend therefrom or be otherwise arranged to lie between the frame and lifting block. A circuit breaker is preferably provided on the frame to be actuated by the striker plate to disconnect the electrical current passing to the motor on an elec- This circuit breaker is arranged to be tripped just prior to or simultaneously with the striker plate contacting the frame. In a preferred form the circuit breaker in addition to cutting off the current to the motor actuates a brake to stop the motors free rotation.

Some of salient features of a preferred form of this invention have been pointed out above, however, additional features and advantages of the invention will become apparent from the following description and the accompanying drawings in which Figure l is a side elevation of a preferred embodiment of my invention as applied to a crane trolley;

Figure 2 is an end elevation of the embodiment illustrated in Figure 1.

Referring to the drawings I have illustrated a crane trolley having a frame it) provided with wheels 11 driven by an electrically-operated drive mechanism 12 and adapted to ride on rails, not shown. An electric motor 13 mounted on the frame it) is provided with a pinion 14 which drives a gear 16 on shaft 15. The intermediate shaft 15 carries a second pinion 17 which engages and drives a gear 18 on a shaft 19 journaled for rotation on the frame and carrying a hoisting drum 20.

A hook block'21 carrying a lifting hook 22 is suspended from the frame 10 by means of a hoisting cable or rope 23. The cable 23 passes over sheave wheels 24 on the trolley frame and sheave wheels 25 in the lifting or hook block 21 in conventional manner and both ends are fixed to and adapted to be wound onto the hoisting drum 20, to lengthen or shorten the cable and thereby raise and lower the hook block 21. A plurality of springs 26 are mounted in pairs on a flange 27 projecting from the side of the hook block 21 and are enclosed within a housing 28 along the side of the hook block above the flange 27. A plunger 29 is mounted on the top of each spring 26 and is adapted to pass into the housing 28. Each such plunger i fixed to a plunger rod 36 passing axially through the center of the spring, through the flange 27 and fitted with a nut 31 preventing the removal of the plunger and spring from the housing 23. Each of the spring and plunger combinations is arranged to be sufficiently compressible to absorb the entire kinetic energy of the moving parts of the hoist without permitting a breaking stress on the hoisting cables 23. A striker plate 32 is mounted on top of and fixed to the plungers 29. It is, of course, obvious that the housing 28 might be dispensed with and replaced by other guide means.

A circuit breaker 33 is mounted on the frame 10 and is provided with a downwardly extending plunger 34 which extends below a lifting beam Ed on the frame 10 in the path of the striker plate 32.

If, when the hook block 21 is being raised by the hoisting drum 2d, the conventional limit switch (not shown) fails to function the hook block is raised until the striker plate 32 engages the plunger 34. The circuit breaker 33 is thereby actuated and a brake 36 is applied to the motor. Immediately after engaging the plunger 34, the striker plate engages the lifting beam 35' and the plungers 2% depress the springs 26 thereby absorbing the energy of the moving parts of the hoist and gradually bringing the hook block to a stop.

In a preferred form the circuit breaker is arranged so that it must be manually reset thus making it necessary for the craneioperator to calla repairman. gives .the crane repairman an opportunity to determine why the conventional limit switch failed to operate.

While l have illustrated and describeda preferred embodiment of my'invention it will be understood that it may be otherwise embodied within'the scope of the following claims.

I claim:

1. A hoisting mechanism comprising a'frame, hoisting ropes depending from said frame, .a lifting block depending from said frame onsaid hoisting ropes, means on the frame raising and lowering said lifting block relative to said frame by varying the length of said ropes, springs positioned on opposite sides of the block and extending verticallytherefrom toward the frame, said springs being of such size as to be capable of absorbing the kinetic energy of the moving lifting block and the raising and lowering means, a striker plate connecting the ends of the springs remote from the block and adapted to engage the frame at any angle of approach capable of being made by the lifting block whereby to engage the frame and absorb the kinetic energy of thelifting block and the raising and lowering means.

2. A hoisting mechanism comprising a frame, hoisting ropes depending from said frame, a lifting blockdepending from said frame on said hoisting ropes, a hoisting drum rotatably mounted on the frame and varying the lengh of said hoisting ropes to raise and lower the lifting block, an electric motor on theframe, driving connections between said motor and the hoisting drum, springs positioned on opposite sides of the block and extending verticaly therefrom toward the frame, said springs being of such size as to be capable of absorbing the kinetic energy of the moving lifting block, the hoisting drum, the electric motor and driving connections, a striker plate conccting the ends of thte springs remote from the block and adapted to engage the frame at any angle of approach capable of being made by the lifting block, a brake on the motor and a circuit breaker mounted on the frame in the motor circuit, a depending plun er extending downwardly from the circuit breaker to a point below the frame in the path of the striker plate whereby to disconnect the motor current and engage the brake on said motor immediately prior to the striker plate engaging the frame.

3. A hoisting mechanism comprising a frame, hoisting ropes depending from said frame, a lifting block depending from said frame on said hoisting ropes, means on the frame raising and lowering said lifting block relative to said fram by varying the length of said ropes, guide means positioned onopposite sides of the bolck and extending vertically therefrom toward the frame, springs in said guide means for movement axially thereof, said springs being of such size as to be capable of absorbing the kinetic energy of the moving lifting block and the raising and lowering means, a striker plate connecting the ends of the springs remote from the block movable vertically with respect to the guide means and adapted to engage the frame at any angle of approach capable of being made by the lifting block whereby to engage theframe and absorb the kinetic energy of'the'lifting blck and the raising and lowering means.

4. A hoisting mechanism 'comprising a frame, hoisting ropes depending from saidframe, alifting block depending from said frame on said hoisting ropes, a hoisting drum rotatably mounted on the frame and varying the length of said hoisting ropes to raise and lower the lifting block, an electric motor on the frame, driving connections between said motor and the hoisting drum, hollow cylindrical guide means positioned on opposite sides of the block and extending vertically therefrom toward the frame, springs in said guide means for movement axially thereof, said springs being of such size as to be capable of absorbing the kinetic energy of'the moving lifting block, the hoisting drum, the electric motor and driving connections, a striker plate above the guide means, connector means connecting the ends of the springs remote from the block to said striker plate, said connector means being adapted to telescope within the guide means and to space the striker plate away from the guide means whereby the striker plate is adapted to engage the frame at any angle of approach capable of being made by the lifting block, a brake on the motor and a circuit breaker mounted on the frame in the motor circuit, a depending plunger extending downwardly from the circuit breaker to a point below the frame in the path of the striker plate whereby to disconnect the motor current and engage the brake on said motor im mediately prior to the striker plate engaging the frame.

References Cited in the file of this patent UNITED STATES PATENTS 876,503 Suliot Jan. 14, 1908 997,934 Pogue July 11, 1911 1,369,147 Valls Feb. 22, 1921 1,848,932 Brinley Mar. 8, 1932 1,965,397 Waechter July 3, 1934 1,975,094 Fitch Oct. 2, 1934 2,020,632 Beeker Nov. 12, 1935 2,529,193 Rueter Nov. 7, 1950

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